Ac light emitting diode and method for fabricating the same

ABSTRACT

The present invention relates to an AC light emitting diode. An object of the present invention is to provide an AC light emitting diode wherein various designs for enhancement of the intensity of light, prevention of flickering of light or the like become possible, while coming out of a unified method of always using only one metal wire with respect to one electrode when electrodes of adjacent light emitting cells are connected through metal wires. To this end, the present invention provides an AC light emitting diode comprising a substrate; bonding pads positioned on the substrate; a plurality of light emitting cells arranged in a matrix form on the substrate; and a wiring means electrically connecting the bonding pads and the plurality of light emitting cells, wherein the wiring means includes a plurality of metal wires connecting an electrode of one of the light emitting cells with electrodes of other electrodes adjacent to the one of the light emitting cells.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/652,555, filed on Jan. 5, 2010, which is a continuation of U.S.patent application Ser. No. 11/997,287, filed on Jan. 29, 2008, which isthe National Stage of International Application No. PCT/KR2006/003016,filed on Aug. 1, 2006, and claims priority from and the benefit ofKorean Patent Application No. 2005-0072828, filed on Aug. 9, 2005, andKorean Patent Application No. 2005-0076874, filed on Aug. 22, 2005,which are all hereby incorporated by reference for all purposes as iffully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an AC (alternating current) lightemitting diode including a plurality of light emitting cells arranged ina matrix form and a method of fabricating the same.

2. Discussion of the Background

A light emitting diode, which is a photoelectric conversion devicehaving a structure in which an N-type semiconductor and a P-typesemiconductor are joined together, emits light through recombination ofelectrons and holes. Such light emitting diodes have been widely used asdisplay devices and backlights. Further, since the light emitting diodehas less electric power consumption and a longer lifetime as comparedwith a conventional light bulb or fluorescent lamp, the light emittingdiode is substituted for a conventional incandescent bulb or fluorescentlamp and has been widely used for the purpose of general illumination.

The light emitting diode is repeatedly turned on/off depending on thedirection of a current under an AC power source. Thus, in a case wherethe light emitting diode is used while connected directly to the ACpower source, there is a problem in that the light emitting diode doesnot continuously light and may easily be damaged by a reverse directioncurrent.

To solve such a problem of the light emitting diode, a light emittingdiode that can be used by connecting it directly to a high-voltage ACpower source has been disclosed in PCT No. WO2004/023568(A1), entitled“LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS” by SAKAI et al.

According to disclosed PCT No. WO2004/023568(A1), light emitting cellsare two-dimensionally connected in series on an insulation substratesuch as a sapphire substrate through metal wires to form LED arrays.Such two LED arrays are in reverse parallel on the substrate. As aresult, the arrays are repeatedly turned on/off alternately by an ACpower supply to emit light.

However, since the disclosed conventional technology is implementedthrough a unified method in which only one metal wire is always usedwith respect to one electrode when connecting electrodes of the adjacentlight emitting cells through metal wires, various designs of AC lightemitting diodes for enhancement of the intensity of light, prevention offlickering of light or the like have been limited.

As an example, if the conventional unified wire connection method isused in a case where the light emitting cells are arranged to constitutea matrix and an additional means for enhancing the intensity of light orthe like is added as a portion of the elements of the matrix, there maybe many difficulties in connecting the metal wires while avoiding theelement added as the element of the matrix. Even though it is possible,there may be caused a problem in that the total length of the metalwires becomes extremely long.

SUMMARY OF THE INVENTION

Further, the disclosed conventional technology is configured such thatthe light emitting cells in the same line are repeatedly turned on/offat the same time, so that continuous and uniform light is not emittedfrom the substrate and thus flickering arises. In a case where the lightemitting diode is used for a long time, such flickering may be a majorcause for making human eyes fatigued although the flickering is notobserved with naked eyes. The present inventors have conducted variousstudies for minimizing the aforementioned flickering, and found that theconventional unified wire connection method of using only one metal wirewith respect to one electrode becomes a large obstacle in theimplementation of a technique for minimizing the flickering.

An object of the present invention is to provide an AC light emittingdiode wherein adaptable designs for enhancement of the intensity oflight, prevention of flickering of light or the like become possible,while breaking from the conventional method of always using only onemetal wire with respect to one electrode when electrodes of adjacentlight emitting cells are connected through metal wires.

Another object of the present invention is to provide an AC lightemitting diode wherein it is easier to employ a means such as a lightguide portion for improvement of the intensity of light, while breakingfrom the conventional method of always using only one metal wire withrespect to one electrode when electrodes of adjacent light emittingcells among light emitting cells arranged as elements of a matrix areconnected through metal wires.

A further object of the present invention is to provide an AC lightemitting diode wherein it is possible to solve disadvantages of theconventional technology, such as flickering of light, while breakingfrom the conventional method of always using only one metal wire withrespect to one electrode when at least a pair of arrays are configuredwith light emitting cells arranged as elements of a matrix.

According to an aspect of the present invention, there is provided an AClight emitting diode comprising: a substrate; bonding pads positioned onthe substrate; a plurality of light emitting cells arranged in a matrixform on the substrate; and a wiring means electrically connecting thebonding pads and the plurality of light emitting cells, wherein thewiring means at least includes a plurality of metal wires connecting anelectrode of one of the light emitting cells with electrodes of otherlight emitting cells adjacent to the one of the light emitting cells.

Preferably, each of the plurality of light emitting cells has first andsecond electrodes of a P-type an N-type, a light emitting cell adjacentto two light emitting cells among the plurality of light emitting cellshas a first electrode connected to a second electrode of one of theadjacent two light emitting cells through a metal wire, and a secondelectrode connected to a first electrode of the other of the adjacenttwo light emitting cells through another metal wire. Wherein, if firstelectrodes are P-type, then second electrodes are N-type. However, iffirst electrodes are N-type, then second electrodes are P-type.

Preferably, each of the plurality of light emitting cells has first andsecond electrodes of a P-type and an N-type, a light emitting celladjacent to three light emitting cells among the plurality of lightemitting cells has a first electrode connected to a second electrode ofone of the adjacent three light emitting cells through a metal wire, anda second electrode connected to first electrodes of the others of theadjacent three light emitting cells through other two metal wires.

Preferably, each of the plurality of light emitting cells has first andsecond electrodes of a P-type and an N-type, a light emitting celladjacent to four light emitting cells among the plurality of lightemitting cells has a first electrode connected to first electrodes oftwo of the adjacent four light emitting cells through two metal wires,and a second electrode connected to second electrodes of the others ofthe adjacent four light emitting cells through other two metal wires.

Preferably, the AC light emitting diode according to the aspect of thepresent invention, further comprises light guide means further formed asan element of the matrix to focus light emitted from the plurality oflight emitting cells adjacent to the at least light guide portion and toradiate the light to the outside. More preferably, the light guide meansconsists of a plurality of light guide portions regularly arranged at apredetermined interval.

According to another aspect of the present invention, there is providedan AC light emitting diode comprising: a substrate; bonding padspositioned on the substrate; a plurality of light emitting cellsarranged as elements of a matrix on the substrate; and a wiring meanselectrically connecting the bonding pads and the plurality of lightemitting cells, wherein the wiring means at least includes two metalwires connecting an electrode of one of the light emitting cells withelectrodes of other light emitting cells adjacent to the one of thelight emitting cells, and the plurality of light emitting cells includeat least a pair of arrays of first and second arrays, and the two metalwires comprise a metal wire connecting the same kinds of electrodes ofadjacent two of the light emitting cells provided in the same first orsecond array and a metal wire connecting first and second electrodes ofadjacent two of the light emitting cells respectively provided in thefirst and second arrays.

According to the present invention, there is an advantage in that it ispossible to design a variety of AC light emitting diodes for enhancingthe intensity of light or minimizing flickering of light through aconfiguration of connecting one electrode of a light emitting cell as anelement of a matrix to electrodes of other light emitting cells adjacentto the light emitting cell or to other matrix elements through two metalwires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 4 are views illustrating arrangements of metal wiring thatcan be applied to an AC light emitting diode according to the presentinvention;

FIG. 5 is a circuit diagram of an AC light emitting diode according to afirst embodiment of the present invention;

FIG. 6 is a plan view of the AC light emitting diode according to thefirst embodiment of the present invention;

FIG. 7 is a sectional view taken along line A-A in FIG. 6;

FIG. 8 is a sectional view taken along line B-B in FIG. 6;

FIGS. 9 and 10 are sectional views illustrating various forms of lightguide portions that may be used in the first embodiment of the presentinvention;

FIGS. 11 to 14 are sectional views illustrating a method of fabricatingthe AC light emitting diode shown in FIGS. 5 to 10;

FIG. 15 is a circuit diagram of an AC light emitting diode according toa second embodiment of the present invention; and

FIG. 16 is a plan view of the AC light emitting diode according to thesecond embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIGS. 1 to 4 are views illustrating arrangements of metal wiring thatcan be used in connection between electrodes of light emitting cells inan AC light emitting diode according to the present invention. As shownin FIGS. 1 to 4, each of light emitting cells 200 is formed with N-typeand P-type electrodes 50 a and 50 b, which are connected to electrodesof other light emitting cells (not shown) adjacent to the light emittingcell 200 through metal wires 400, respectively. In the descriptions ofFIGS. 1 to 4, the N-type electrode 50 a is referred to as a firstelectrode 50 a and the P-type electrode 50 b is referred to as a secondelectrode 50 b for convenience of illustration. Further, the termadjacent elements used throughout the specification indicate onlyelements adjacent left and right or above and below and not elementsadjacent diagonally.

Referring to FIG. 1, a metal wire 400 is connected to a first electrode50 a of one of the light emitting cells 200, and another metal wire 400is also connected to a second electrode 50 b thereof. The arrangement ofsuch metal wires 400 and 400 are usefully utilized in connecting thefirst and second electrodes 50 a and 50 b of the one of the lightemitting cells 200 adjacent to two light emitting cells among theplurality of light emitting cells constituting a matrix to electrodes ofthe adjacent light emitting cells. At this time, in a case where thereis a bonding pad 300 a or 300 b (see FIGS. 5 and 6) among the elementsof the matrix, which will be described in detail below, one of the metalwires 400 and 400 respectively connected to the first and secondelectrodes 50 a and 50 b can be connected to the bonding pad adjacent tothe light emitting cell 200.

Referring to FIG. 2, a metal wire 400 is connected to a second electrode50 b of one of the light emitting cells 200, while two metal wires 400and 400 are connected to a first electrode 50 a thereof. The two metalwires 400 and 400 are used in respectively connecting the firstelectrode 50 a provided in the one of the light emitting cells 200 toelectrodes of other two light emitting cells adjacent to the one of thelight emitting cells 200 or to an electrode of one of the two lightemitting cells adjacent to the one of the light emitting cells 200 and abonding pad.

Referring to FIG. 3, a metal wire 400 is connected to a first electrode50 a of one of the light emitting cells 200, while two metal wires 400and 400 are connected to a second electrode 50 b thereof. The two metalwires 400 and 400 are used in respectively connecting the secondelectrode 50 b provided in the one of the light emitting cells 200 toelectrodes of other two light emitting cells adjacent to the one of thelight emitting cells 200 or to an electrode of one of the two lightemitting cells adjacent the one of the light emitting cells 200 and abonding pad.

Since the arrangements of the metal wiring shown in FIGS. 2 and 3 arethose in which two metal wires 400 and 400 are connected from anelectrode (first or second electrode) of the one of the light emittingcells 200 and a metal wire 400 is connected from the other electrode,the arrangements may be preferably used in connection of the metalwiring when the light emitting cells 200 are arranged as elements of amatrix and adjacent to three matrix elements (light emitting cells, or alight emitting cell and a bonding pad).

Similarly to the arrangements shown FIGS. 2 and 3, also in FIG. 4, thereis shown the arrangement of the metal wiring in which two metal wires400 and 400 are connected to each electrode of a light emitting cell200. In the arrangement of the metal wiring shown in FIG. 4, two metalwires are connected to each of two electrodes of one of the lightemitting cells 200, i.e., each of first and second electrodes 50 a and50 b. The metal wires of which two are connected to each of the firstand second electrodes 50 a and 50 b, i.e. all four metal wires areconnected to matrix elements adjacent to the one of the light emittingcells 200 above, below, left and right, respectively. Further, in a casewhere the adjacent matrix element is a light emitting cell, the metalwire 400 is connected to an electrode of the light emitting cell, and ina case where the adjacent matrix element is a bonding pad, the metalwire 400 is connected to the bonding pad itself.

An AC light emitting diode according to a first embodiment of thepresent invention that can be obtained through the arrangements of themetal wiring shown FIGS. 1 to 4, is shown in FIGS. 5 and 6 respectivelyas a circuit diagram and a plan view. In FIG. 6, the arrangements of themetal wires shown in FIGS. 1 to 4 are formed in circles C″, D″, E″, andF″ respectively.

That is, in circle C″ of FIG. 6 is shown an arrangement in which a metalwire 400 is connected to each of first and second electrodes 50 a and 50b of one of the light emitting cells 200, and the respective metal wires400 are connected to second and first electrodes 50 b and 50 a of otherlight emitting cells adjacent to the one of the light emitting cells200. In circle D″ of FIG. 6 is shown an arrangement in which two metalwires 400 and 400 connected to a first electrode 50 a of one of thelight emitting cells 200 are respectively connected to second electrodes50 b and 50 b of two light emitting cells adjacent to the one of thelight emitting cells 200, and a metal wire 400 connected to a secondelectrode 50 b of the one of the light emitting cells 200 is connectedto a first electrode 50 a of another light emitting cell adjacent to theone of the light emitting cells 200. In circle E″ of FIG. 6 is shown anarrangement in which two metal wires 400 and 400 connected to a secondelectrode 50 b of one of the light emitting cells 200 are respectivelyconnected to first electrodes 50 a and 50 a of two light emitting cellsadjacent to the one of the light emitting cells 200, and a metal wire400 connected to a first electrode 50 a of the one of the light emittingcells 200 is connected to a second electrode 50 b of another lightemitting cell 200 adjacent to the one of the light emitting cells 200.In circle F″ of FIG. 6 is shown an arrangement in which two metal wiresconnected to a second electrode 50 b of one of the light emitting cells200 are respectively connected to first electrodes 50 a and 50 a of twolight emitting cells adjacent to the one of the light emitting cells200, and two metal wires connected to a first electrode 50 a of the oneof the light emitting cells 200 are respectively connected to secondelectrodes 50 b and 50 b of other two light emitting cells adjacent tothe one of the light emitting cells 200. At this time, although thefirst electrode 50 a is shown as if it is two electrodes in circle F″ ofFIG. 6, it should be noted that the first electrode 50 a is practicallyone identical electrode.

As shown in FIGS. 5 and 6, the AC light emitting diode according to thisembodiment comprises a substrate 100, light emitting cells 200, firstand second bonding pads 300 a and 300 b, metal wires 400, and lightguide portions 500.

The substrate 100 may be made of a sapphire or material such as SiC withthermal conductivity larger than a sapphire, and the plurality ofpatterned light emitting cells 200 are formed on the substrate 100.

FIG. 7 is a sectional view taken along line A-A in FIG. 6. Referring toFIG. 7, each of the light emitting cells 200 forms a structure in whichan N-type semiconductor layer 31, an active layer 32 and a P-typesemiconductor layer 33 are sequentially laminated. The active layer 32is formed on a portion of the N-type semiconductor layer 31, and theP-type semiconductor layer 33 is formed on the active layer 32. Thus,the portion of a top surface of the N-type semiconductor layer 31 isjoined with the active layer 32, and the other portion of the topsurface is exposed to the outside.

Referring back to FIGS. 5 and 6, the light emitting cells 200 arearranged between the first and second bonding pads 300 a and 300 b inthe form of a matrix, e.g., a square matrix.

The first and second bonding pads 300 a and 300 b are to connect a lightemitting diode 1 to an external power source through the metal wires400. The first and second bonding pads 300 a and 300 b may be connectedto the external power source through bonding wires (not shown).

The metal wires 400 electrically connect the light emitting cells 200.Each of the metal wires 400 connects a first electrode 50 a of one ofthe light emitting cells 200 to a second electrode 50 b of another lightemitting cell 200 adjacent to the corresponding light emitting cell 200,so that P-type and N-type semiconductor layers 33 and 31 of the adjacentlight emitting cells 200 are electrically connected to each other. Also,each of the metal wires 400 electrically connects a first or secondelectrode 50 a or 50 b of one of the light emitting cells 200 to thefirst or second bonding pad 300 a or 300 b adjacent to the correspondinglight emitting cell 200 thereby to supply power to the light emittingdiode 1.

Some of the metal wires 400 connect first and second electrodes 50 a and50 b of one of the light emitting cells 200 positioned at anintersection where a row and a column meet each other to second andfirst electrodes 50 b and 50 a of light emitting cells adjacent to theone of the light emitting cells 200, respectively. Also, some of themetal wires 400 electrically connect the bonding pad 300 a or 300 bpositioned at an intersection where a row and a column meet each otherto first and second electrodes 50 a and 50 b of light emitting cellsadjacent to the one of the light emitting cells 200.

Particularly, one of the light emitting cells 200 positioned adjacent totwo matrix elements among the light emitting cells 200 has a firstelectrode 50 a electrically connected to a second electrode 50 b of alight emitting cell 200 adjacent to the one of the light emitting cells200 or the bonding pad 300 a or 300 b, and a second electrode 50 belectrically connected to a first electrode 50 a of another lightemitting cell 200 adjacent to the one of the light emitting cells 200 orthe bonding pad 300 a or 300 b.

In the matrix arrangement, two of the metal wires 400 are required in acase where the number of matrix elements (except light guide portions)positioned adjacent to one of the light emitting cells 200 is two. Afirst electrode 50 a of one of a light emitting cell 200 should beconnected to a second electrode 50 b of another of the light emittingcells 200 for the purpose of operating a diode. Thus, there is only thesame arrangement of the metal wiring as shown in FIG. 1.

In the matrix arrangement, in a case where the number of matrix elements(except light guide portions) positioned adjacent to one of the lightemitting cells is three, a first electrode 50 a of the correspondinglight emitting cell 200 may be connected to any one of a secondelectrode 50 b of a light emitting cell 200 adjacent to thecorresponding light emitting cell 200 and the bonding pad 300 a or 300 bthrough a metal wire 400, and a second electrode 50 b of thecorresponding light emitting cell 200 may be connected to firstelectrodes 50 a of two light emitting cells 200 adjacent to thecorresponding light emitting cell 200 or a first electrode 50 a of alight emitting cell adjacent to the corresponding light emitting cell200 and the bonding pad 300 a or 300 b through two metal wires 400 and400.

Further, in a case where the number of matrix elements (except lightguide portions) positioned adjacent to one of the light emitting cellsis three as described above, a first electrode 50 a of the correspondinglight emitting cell 200 may be electrically connected to secondelectrodes 50 b of two light emitting cells 200 adjacent to thecorresponding light emitting cell 200 or a second electrode 50 b of alight emitting cell adjacent to the corresponding light emitting cell200 and the bonding pad 300 a or 300 b through two metal wires 400 and400, and a second electrode 50 b of the corresponding light emittingcell 200 may be electrically connected to any one of a second electrode50 b of another light emitting cell 200 adjacent to the one of the lightemitting cells 200 and the bonding pad 300 a or 300 b through one metalwire 400.

That is, in the matrix arrangement, in a case where the number of matrixelements (except light guide portions) positioned adjacent to a lightemitting cell is three, the aforementioned three metal wires 400 for thecorresponding light emitting cell are required for the purpose ofoperating a diode (see FIGS. 2 and 3).

Also, a first electrode 50 a of one of the light emitting cells 200positioned adjacent to four of the light emitting cells 200 iselectrically connected to second electrodes 50 b of two of the fourlight emitting cells 200 adjacent to the corresponding light emittingcell 200, and a second electrode 50 b of the corresponding lightemitting cell is electrically connected to first electrodes 50 a of theother two light emitting cells 200 adjacent thereto. In addition, afirst electrode 50 a of one of the light emitting cells 200 positionedadjacent to three of the light emitting cells 200 and one of the bondingpads 300 a and 300 b is electrically connected to second electrodes 50 bof two of the three light emitting cells 200 adjacent to thecorresponding light emitting cell 200, and a second electrode 50 b ofthe corresponding light emitting cell is electrically connected to afirst electrode 50 a of another light emitting cell 200 adjacent theretoand the bonding pad 300 a or 300 b; alternatively, the first electrode50 a of the corresponding light emitting cell 200 is electricallyconnected to a second electrode 50 b of one of the three light emittingcells 200 adjacent to the corresponding light emitting cell 200 and thebonding pad 300 a or 300 b, and the second electrode 50 b of thecorresponding light emitting cell is electrically connected to firstelectrodes 50 a of the other two light emitting cells 200 adjacent tothe corresponding light emitting cell 200.

In the matrix arrangement, in a case where the number of matrix elements(except light guide portions) positioned adjacent to one of the lightemitting cells is four, a pair of metal wires are required for eachelectrode of the corresponding light emitting cell 200, that is a totalof four metal wires 400 are required, and a first electrode 50 a of thecorresponding light emitting cell 200 should be connected to secondelectrodes 50 b of other light emitting cells 200 for the purpose ofoperating a diode (see FIG. 4).

The light guide portions 500 are formed to be arranged together with thelight emitting cells 200 and the bonding pads 300 a and 300 b in amatrix form, and function to guide light emitted from a plurality of thelight emitting cells 200, which are positioned adjacent to the lightguide portions 500, to be focused and radiated to the outside.Particularly, it is preferred that the light guide portions 500 beregularly arranged to be spaced apart from each other at predeterminedintervals and thus a fabricating process of the light emitting diode 1can be simplified and fabricating costs can be reduced.

It will be apparent that a shape of the light guide portion 500 asviewed from above may have an angled shape such as a quadrangle orpentagon although it is a circle as shown in FIG. 6.

Referring back to FIG. 7, the light emitting cells 200 spaced apart fromone another are positioned on the substrate 100. Each of the lightemitting cells 200 comprises the N-type semiconductor layer 31, theP-type semiconductor layer 33 positioned over a portion of the N-typesemiconductor layer 31, and the active layer 32 interposed between theN-type and P-type semiconductor layers 31 and 33. Here, the N-typesemiconductor layer 31 serves as a first electrode 50 a. Meanwhile, asecond electrode 50 b is formed on the P-type semiconductor layer 33.The second electrode 50 b may be a transparent electrode layer 40through which light can be transmitted. The light emitting cells 200 maybe formed by forming the respective semiconductor layers 30 and thetransparent electrode layer 40 on the substrate 100 and then patterningthem using a photo and etching process. An electrode pad 60 b may beformed on the other portion of the N-type semiconductor layer 31, and anelectrode pad 60 a may be formed on the second electrode 40. Theelectrode pads 60 a and 60 b may be formed at a desired position using alift-off technique. The metal wires 400 may be formed together using anair-bridge or step-cover process.

FIG. 8 is a partial sectional view taken along line B-B in FIG. 6.Referring to FIG. 8, the light emitting cells 200 spaced apart from eachother are positioned on the substrate 100, and one of the light guideportions 500 is positioned between the light emitting cells 200. Thelight emitting cells 200 have the same configuration as the lightemitting cells 200 shown in FIG. 7. The light guide portion 500 may beformed by forming the semiconductor layers 30 and the transparentelectrode layer 40 and then etching a central portion thereof such thatthe substrate 100 is exposed. The light guide portion 500 may be etchedsuch that the central portion has a slope with respect to the substrate100 as shown in FIG. 9 or becomes vertical to the substrate 100 as shownin FIG. 10. The light guide portion 500 serves to guide the collectedlight in a predetermined direction, e.g., a vertical direction to thesubstrate, after collecting the light emitted from the light emittingcells 200 adjacent to the light guide portion 500.

If only the light emitting cells 200 are arranged without the lightguide portions 500 in a case where the light emitting cells 200 arearranged in rows and columns, e.g., a two-dimensional square shape, theluminance of light progressing in the horizontal direction with respectto the substrate 100 among the light emitted from the light emittingcells 200 is decreased as the light passes through the light emittingcells 200 adjacent thereto, so that the entire light emitting efficiencyof the light emitting diode 1 is lowered. Accordingly, the light guideportions 500 are arranged at predetermined intervals to collect lightincident in the horizontal direction from the light emitting cells 200adjacent thereto and to radiate the light in the vertical direction asshown in FIGS. 5 and 6, thereby enhancing the light emitting efficiencyof the light emitting diode 1.

In addition, a light reflection prevention layer 70 may be formed in thelight guide portion 500 by coating the light guide portion 500 with alight reflection prevention substance for enhancing the lighttransmittance of the light guide portion 500. Preferably, the thicknessof the light reflection prevention layer is λ/4n. Here, λ is awavelength of light incident from the light emitting cell adjacent tothe light guide portion 500, and n is a refractive index of the lightreflection prevention substance. Preferably, the light reflectionprevention substance is to have a refractive index of 1.3 to 1.7. Forexample, the light reflection prevention substance may be SiO.sub.2,Al.sub.2O.sub.3 or Si.sub.3N.sub.4. The light reflection preventionlayer 70 may be formed by sputtering the light reflection preventionsubstance on the light guide portion 500.

A method of fabricating the aforementioned AC light emitting diode willbe described below with reference to FIGS. 11 to 14.

Referring to FIG. 11, a buffer layer 20 is formed on the substrate 100,and then the N-type semiconductor layer 31, the active layer 32, theP-type semiconductor layer 33 and the transparent electrode 40 aresequentially laminated on the buffer layer 20. The buffer layer 20 andthe semiconductor layers 30 may be formed using a metal organic chemicalvapor deposition (MOCVD), molecular beam epitaxy (MBE) or hydride vaporphase epitaxy (HVPE) technique. Further, the semiconductor layers 30 maybe consecutively formed in the same process chamber. Although the bufferlayer 20 may be formed of an insulation substance film such as an AlN orsemi-insulation GaN layer, it may also be made of a conductive substancefilm such as an N-type GaN layer if necessary. The transparent electrodelayer 40 may be a transparent electrode layer made of Ni/Au or indiumtin oxide (ITO).

Referring to FIG. 12, after the transparent electrode layer 40 isformed, the semiconductor and transparent electrode layers 30 and 40 arepatterned using photo and etching processes, thereby formingsemiconductor patterns 200 and 500 arranged in a matrix form and spacedapart from one another.

After the semiconductor patterns 200 and 500 are formed, the P-typesemiconductor layer 33 and the active layer 32 are patterned in the formof semiconductor patterns to be fabricated as light emitting cells 200among the semiconductor patterns 200 and 500 using photo and etchingprocesses such that a portion of a top of the N-type semiconductor layer31 is exposed. Referring to FIG. 13, thereafter, by performing apatterning process on semiconductor patterns to be fabricated as a lightguide portion 500 among the semiconductor patterns 200 and 500, thelight guide portion 500 is formed which has an outer circumferentialportion on which light is incident from the light emitting cells 200adjacent to the light guide portion 500 and an inner circumferentialportion for guiding the incident light to be radiated in a predetermineddirection. Then, an electrode pad 60 b (see FIG. 7) is formed on theexposed N-type semiconductor layer 31. The electrode pad 60 b may beformed using a lift-off method. Thereafter, the electrode pads 60 b and60 a (see FIG. 7) of the light emitting cells adjacent to each other areconnected through the metal wires 400. The metal wires 400 may be formedthrough an air-bridge or step-cover process.

Referring to FIG. 14, after the light guide portion 500 is formed, alight reflection prevention layer 70 covering the surface of the lightguide portion 500 except the outer circumferential portion is formed bysputtering a light reflection prevention substance on the light guideportion 500 in order to increase the light transmittance of lightincident on the light guide portion 500. The light reflection preventionsubstance may be SiO.sub.2, Al.sub.2O.sub.3 or Si.sub.3N.sub.4, and thethickness of the light reflection prevention layer 70 may be λ/4n. Here,λ is a wavelength of light incident from the light emitting cell 200adjacent to the light guide portion 500, and n is a refractive index ofthe light reflection prevention substance.

Although it has been described in the aforementioned embodiment that thelight guide portion 500 is formed after the transparent electrode layer40 is formed, it will be apparent that the light guide portion 500 maybe formed after the semiconductor layers 30 are formed.

Hereinafter, an AC light emitting device according to a secondembodiment of the present invention will be described with reference toFIGS. 15 and 16. The same components as the aforementioned firstembodiment of the present invention, i.e., the substrate, the first andsecond electrodes, and the first and second bonding pads will use likereference numerals used in the aforementioned first embodiment of thepresent invention. However, the reference numerals of metal wires willbe used by dividing them into “400 a” “400 b” “400 c” “400 d” and “400e” depending on use contrary to the aforementioned embodiment. Thesecond embodiment of the present invention will be completed byemploying the configuration in which an electrode of one of the lightemitting cells is connected to electrodes of other two light emittingcells adjacent to the one of the light emitting cells 200 through twometal wires as shown in FIGS. 2 and 3.

Referring to FIGS. 15 and 16, the AC light emitting diode 1 of thisembodiment has at least a pair of first and second arrays 11 and 13 oflight emitting cells 200. Here, two pairs of the arrays 11 and 13 areshown. Such a pair of arrays is aligned to be adjacent to each other.

Metal wires 400 a and 400 b shown in FIG. 16 electrically connect thelight emitting cells 200 arranged between the light emitting cells atboth ends of each of the arrays. At this time, the metal wires 400 a and400 b electrically connect first and second electrodes 50 a and 50 b ofone of the light emitting cells to a first electrode 50 a of one of twolight emitting cells adjacent to the one of the light emitting cells 200and a second electrode 50 b of the other of the two light emitting cellsadjacent thereto, so that the light emitting cells in each of the arraysare connected to one another.

The metal wires 400 b for connecting the second electrodes 50 b of thefirst array 11 are adjacent to the metal wires 400 a for connecting thefirst electrodes 50 a of the second array 13, and the metal wires 400 afor connecting the first electrodes 50 a of the first array 11 areadjacent to the metal wires 400 b for connecting the second electrodes50 b of the second array 13.

As well shown in FIG. 16, the light emitting cells 200 are arranged sothat facing electrodes of adjacent two of the light emitting cells 200provided in the same array 11 or 13 are the same kind as the firstelectrode 50 a or the second electrode 50 b, and facing electrodes ofadjacent two of the light emitting cells respectively provided in thefirst and second arrays 11 and 13 are different kinds from each other asthe first and second electrodes 50 a and 50 b. Such arrangements enablethe total length of the metal wires to be reduced and the metal wires tobe easily connected.

For example, in a case where one of the light emitting cells 200 has thesecond and first electrodes 50 b and 50 a sequentially formed along thefirst array 11, the two light emitting cells adjacent to the one of thelight emitting cells 200 in the same array 11 respectively have thefirst and second electrodes 50 a and 50 b sequentially formed along thefirst array 11. Accordingly, the length of the metal wires 400 a and 400b connecting the light emitting cells 200 in the same array can bereduced. Further, the light emitting cells of the second array 13adjacent to the first array 11 are arranged in the opposite direction ofthe light emitting cells of the first array 11. That is, a lightemitting cell 200 of the second array 13, which is adjacent to a lightemitting cell 200 of the first array 11 that has the first and secondelectrodes 50 a and 50 b in turn along the first array 11, are arrangedto have the second and first electrodes 50 b and 50 a in turn along thesecond array 13.

Meanwhile, metal wires 400 c and 400 d electrically connect the wiringconnections between the first electrodes 50 a and 50 a of the firstarray 11 to the adjacent wiring connections between the secondelectrodes 50 b and 50 b of the second array 13, respectively, andelectrically connect the wiring connections between the secondelectrodes 50 b and 50 b of the first array 11 to the adjacent wiringconnections between the first electrodes 50 a and 50 a of the secondarray 13, respectively. For the electrical connection between theaforementioned wiring connections, the metal wires 400 c and 400 dconnect the first and second electrodes 50 a and 50 b of each of thelight emitting cells 200 of the first array 11 to the adjacent secondand first electrodes 50 b and 50 a of each of the light emitting cellsof the second array 13, respectively. More specifically, the firstelectrode 50 a of one of the light emitting cells of the first array 11and the second electrode 50 b of the light emitting cell of the secondarray 13 adjacent thereto are connected to each other through the metalwire 400 c, and the second electrodes 50 b of the light emitting cellsadjacent to the one of the light emitting cells in the first array 11the first electrodes 50 a of the light emitting cells in the secondarray 13 adjacent thereto are connected to each other through the metalwires 400 d.

The aforementioned arrangement of the metal wires 400 a, 400 b, 400 cand 400 d can be performed by connecting two metal wires to oneelectrode 50 a or 50 b of the corresponding light emitting cell 200 andby connecting the two metal wires to electrodes of other light emittingcells adjacent to the corresponding light emitting cell. The connectionof such metal wires has been already described in detail in theaforementioned descriptions of FIGS. 2 and 3.

Meanwhile, the bonding pads 300 a and 300 b may be arranged on thesubstrate 100 near both the ends of the arrays 11 and 13. The bondingpads 300 a and 300 b are to connect the AC light emitting diode 1 to anexternal power source. The bonding pads 300 a and 300 b may be connectedto the external power source through bonding wires (not shown), or maybe flip-chip bonded to a submount to be connected to the external powersource.

Metal wires 400 e can connect the bonding pads 300 a and 300 b and thelight emitting cells at both the ends of the first and second arrays 11and 13. Accordingly, the light emitting cells in a pair of the arrays 11and 13 are connected zigzag to each other to be driven under an AC powersource.

According to this embodiment, since the light emitting cells of thefirst and second arrays 11 and 13 operate in a zigzag fashion, the lightemitting cells of this embodiment may emit generally uniform light ascompared with a prior art operating on a substrate in an array unit.

Meanwhile, although it has been described in this embodiment that thelight emitting cells at both the ends of each of the arrays 11 and 13are all connected to the bonding pads 300 a and 300 b through the metalwires 400 e, it is not limited thereto and the light emitting cells atboth ends of the arrays may be connected to the bonding pads 300 a and300 b after a plurality of arrays are connected through metal wires.

Although the present invention has been described in detail inconnection with the specific embodiments, it will be readily understoodby those skilled in the art that various modifications and changes canbe made thereto within the technical spirit and scope of the presentinvention. Accordingly, it should be construed that the aforementioneddescriptions and drawings do not limit the technical spirit of thepresent invention but illustrate the present invention.

1. A light emitting device, comprising: a plurality of light emittingcells arranged on a single substrate; a light emitting diode blockcomprising at least a light emitting cell of the plurality of lightemitting cells; four light emitting diode arrays each comprising atleast a light emitting cell of the plurality of light emitting cells;and two electrodes arranged on the substrate to supply power to thelight emitting diode block and the light emitting diode arrays, whereina first electrode of the light emitting cell positioned at one end ofthe light emitting diode block is coupled to a second electrode of eachof the light emitting cells positioned at one side end of two of thelight emitting diode arrays, and wherein a second electrode of the lightemitting cell positioned at another end of the light emitting diodeblock is coupled to a first electrode of each of the light emittingcells positioned at one side end of the other two of the light emittingdiode arrays.
 2. The light emitting device of claim 1, wherein the twoelectrodes are arranged at diagonally opposite corners of the substratefrom each other.
 3. The light emitting device of claim 1, wherein thelight emitting device is configured to operate on alternating current(AC) power.
 4. The light emitting device of claim 3, wherein the lightemitting diode block is configured to emit light in response toapplication of both a forward bias cycle of the AC power and a reversebias cycle of the AC power.
 5. The light emitting device of claim 3,wherein one of the light emitting diode arrays coupled to the firstelectrode of the light emitting cell positioned at the one end of thelight emitting diode block, the light emitting diode block, and one ofthe light emitting diode arrays coupled to the second electrode of thelight emitting cell positioned at the other end of the light emittingdiode block are configured to emit light in response to application of aforward bias cycle of the AC power; and wherein the other one of thelight emitting diode arrays coupled to the second electrode of the lightemitting cell positioned at the other end of the light emitting diodeblock, the light emitting diode block, and the other one of the lightemitting diode arrays coupled to the first electrode of the lightemitting cell positioned at the one end of the light emitting diodeblock are configured to emit light in response to application of areverse bias cycle of the AC power.
 6. The light emitting device ofclaim 4, wherein one of the light emitting diode arrays coupled to thefirst electrode of the light emitting cell positioned at the one end ofthe light emitting diode block, the light emitting diode block, and oneof the light emitting diode arrays coupled to the second electrode ofthe light emitting cell positioned at the other end of the lightemitting diode block are configured to emit light in response toapplication of the forward bias cycle of the AC power; and wherein theother one of the light emitting diode arrays coupled to the secondelectrode of the light emitting cell positioned at the other end of thelight emitting diode block, the light emitting diode block, and theother one of the light emitting diode arrays coupled to the firstelectrode of the light emitting cell positioned at the one end of thelight emitting diode block are configured to emit light in response toapplication of the reverse bias cycle of the AC power.
 7. The lightemitting device of claim 1, further comprising a first serial arrayconnected in parallel to a second serial array, the first serial arraycomprising the light emitting cells of the light emitting diode blockand two of the light emitting diode arrays.